Color image density calibration in imaging device having common developer voltage

Abstract

A color imaging device includes a plurality of developer rolls with a common operating point, such as a common operating voltage. To determine the operating point, an acceptable range of color density is determined for each toner, the range being lighter and darker than an optimum color density for that toner. A search range is devised such that values within the range are examined relative to deviations from the optimum color density per each toner. The common operating point is selected as that having the lowest deviation per all toners. Also, if the common operating point corresponds to a color density darker than the acceptable range of color density for any toner, additional halftoning occurs compared to traditional halftoning, such as for continuous tones or solids. In this way, four color developer rolls can be operated from a single power supply, yet still provide acceptable color images.

The invention claimed is: 
     
       1. In an imaging device with a plurality of developer rolls having a common operating point, a method comprising:
 determining an acceptable range of color density for each toner associated with the developer rolls, each said acceptable range of color density being lighter and darker than an optimum color density for said each toner; 
 selecting the common operating point; and 
 if the common operating point corresponds to a color density darker than the acceptable range of color density for any toner of said each toner, halftoning imaging for said any toner. 
 
     
     
       2. The method of  claim 1 , further including determining an amount of halftoning. 
     
     
       3. The method of  claim 2 , further including for said each said acceptable range of color density, determining an amount of error from the optimum color density, the amount of error corresponding to the amount of halftoning. 
     
     
       4. The method of  claim 3 , further including storing the correspondence between the amount of the error and the amount of halftoning. 
     
     
       5. The method of  claim 1 , wherein said each toner associated with the developer rolls includes black toner and one of cyan toner, magenta toner, and yellow toner. 
     
     
       6. The method of  claim 1 , wherein the selecting the common operating point further includes setting a common voltage for each of said plurality of developer rolls. 
     
     
       7. The method of  claim 6 , wherein the common voltage is provided by a single power supply. 
     
     
       8. The method of  claim 1 , further including creating a patch of toner for said each toner and determining an optical density thereof. 
     
     
       9. The method of  claim 8 , further including correlating the optical density to an operating point of the developer roll. 
     
     
       10. The method of  claim 8 , further including correlating the optical density to luminance for said each toner. 
     
     
       11. In an imaging device with four developer rolls having a common operating voltage, a method comprising:
 determining an acceptable range of color density for color toners associated with the four developer rolls, including cyan toner, magenta toner, yellow toner and black toner respectively, each said acceptable range of color density being lighter and darker than an optimum color density for each of the color toners; 
 selecting the common operating voltage; and 
 if the common operating voltage corresponds to a color density darker than the acceptable range of color density for any of the color toners, halftoning imaging for said any of the color toners. 
 
     
     
       12. The method of  claim 11 , further including determining an amount of halftoning for said any of the color toners. 
     
     
       13. The method of  claim 12 , further including determining an amount of error from the optimum color density for said any of the color toners, the amount of error corresponding to the amount of halftoning. 
     
     
       14. The method of  claim 13 , further including storing the correspondence between the amount of the error and the amount of halftoning. 
     
     
       15. The method of  claim 11 , further including defining a search range for finding the common operating voltage based on each of the acceptable ranges of color density for the color toners. 
     
     
       16. The method of  claim 15 , further including for multiple values corresponding to the search range, determining an amount of error from the optimum color density for each of said color toners. 
     
     
       17. The method of  claim 16 , further including summing together the amounts of error for said each of the color toners. 
     
     
       18. The method of  claim 17 , further including selecting as the common operating voltage within the search range the voltage that has the lowest summation. 
     
     
       19. The method of  claim 11 , wherein the common operating voltage is applied from a single power supply. 
     
     
       20. The method  11 , further including creating a patch of toner for each of said color toners and determining an optical density thereof.